Method for cleaning diffuser tubes



Aug. 1 M. A. LAMB ETAL 2,686,139

METHOD FOR CLEANING DIFFUSER TUBES Filed Dec. 29, 1949 2 Sheets-Sheet l Aug. 10, 1954 LAMB ETAL 2,686,139

METHOD FOR CLEANING DIFFUSER TUBES Filed Dec. 29, 1949 2 Sheets-Shet 2 Patented Aug. 10, 1954 UNITED STATES PATENT OFFICE .METHOD FOR CLEANING DIFFUSER TUBES- Miles A. Lamb, Chicago, and Joseph J. Klein, Glencoe, 'Ill., assignors to Chicago Pump Company, a corporation of Delaware Application December 29, 1949, Serial No. 135,782

'9 Claims. 1

This invention relates to amethod for cleaning diffuser tubes used for theaeration .of liquids .or for the dispersion of gases or vapors therein. More specifically, the invention relates .to the cleaning of diffuser tubes in which the air or gas is supplied under pressure and passes through pores in the tube into the liquid. The invention has particular adaptability to the cleaningof the type of tube in which .the pores are formed by tight windings of non-circular twisted cord wound upon a tubular core, such as is disclosed in the ,co-pending application of Carl .Nordell, which issued as Patent .No. 2,555,201 .on May 29, 1951.

The cleaning of diffuser tubes presents .a substantial problem in the operation of plants emplaying such tubes, for example plants engaged in the activated sludge process of treating sewage. In the course of time, .such diffuser tubes become badly contaminated with sediment and grease, both due to deposits of solid matter from the liquids in which the tubes are placed, and to impurities such as dust and grease in the input air which is diffused through the tube. When the minute pores of the .tube are thus blocked, the pressuredrop .across the .porous medium, and thus the volume .of flow for any given input air pressure, are seriously reduced. Thus with the passage of time the efficiency Of the aeration process in which the tube is employed is greatly impaired. It thus becomes necessary to periodically clean the diffuser tubes to restore the pores to their original condition.

The methods and apparatus for cleaning such diffuser tubes heretofore in common use have required the expenditure of extensive time by trained personnel for-adequate cleaning. .Inaddition to the time required, many of the methods heretofore employed required the use of strong acid or alkaline cleaning solutions, thus requiring special handling and protection of personnel in the cleaning of the tubes, and further adding to the cost of the cleaning operation.

The present invention provides .a method whereby the tubes may be cleaned rapidly and inexpensively. By the method of the present .in-

vention, the amount of labor required in the cleaning of the tubes is made small. Furthermore, the present invention completely eliminates the useof strong and potentially harmful cleaning solutions in the cleaning of such diff-user tubes. Additionally, the apparatus for cleaning such tubes provided in accordance with the invention is extremely simple and inexpensive both to manufacture and to operate.

For a full understanding of the invention, reference is made to .the illustrative embodiment shown in the drawings, in which:

Figure 1 is an elevational view, partly in section, of a diffuser tube, showing the manner vof attachment to an air inlet header;

Fig. .2 is a transverse sectional view of the diffuser tube of Fig. 1, taken along the line 2-2 in the direction indicated by arrows;

Fig. 3 is an enlarged fragmentary sectional view taken along the line 33 .of Fig. 2 in the clirection indicated by arrows;

Fig. 4 is an enlarged fragmentary view, partlally in elevation and partially in section, taken along the line 44 of Fig. 3 in the direction indicated by arrows;

Fig. 5 is a plan view of .a cleaning apparatus embodying the present invention;

Fig. 6 is a vertical sectional view of the cleani-ng apparatus of Fig. 5, taken substantially along the line 5-6 of Fig. 5 in the direction indicated by arrows, and illustrating the manner of performing a portion of the cleaning operation of the invention;

Fig. 7 is an enlargedsectional View of a portion of the cleaning apparatus taken along the line l'! of Fig. 6 in the-direction indicated by arrows; and

Fig. '8 is a vertical sectional view taken along the line 88 .of Fig. 7, and illustrating the manner of disposition in the apparatus of a diffuser tube subjected to a-step in the cleaning process of the invention.

One type of difiuser tube .now in common use is the diffuser tube of the general type described in Patent N 0. 2,555,201 of May 29, 1951. This type of diffuser tube has achieved substantial success, particularly in the activated sludge process for treating sewage, because of its simplicity and inexpensiveness and its feficiency in diffusion of air. However, the cleaning of diffuser tubes of this type has proven to be a vexing problem. Although such diffuser tubes are not in themselves any part of the present invention, an example :of such a diffuser tube is illustrated in Figs. 1 through 4 of the drawing and described below in order to facilitate understanding of the difficulties encountered in cleaning such tubes, and to further facilitate understanding of the manner in which the cleaning problem of this tube and other diffuser tubes, such as those made from ceramic material or carbon, may be solved bythe process and apparatus of the present inven- .tion.

Referring first to Fig. 1, the reference numeral it indicates an air main having an opening 12 into which the open end of a diffuser tube, generally indicated by the numeral 14, is threaded. The diffuser tube 54 comprises a hollow core l6 of steel or other suitable material, depending upon the characteristics of the materials with which it is designed to come in contact, a winding [8 of cord which covers virtually the entire core and a pair of end caps 28 and 22, which may be formed of the same material as the core. The core i6 is an open ended cylindrical tube to the ends of which caps 26 and 22 are secured in any suitable manner, preferably by welding. The ends of the winding cord [8 are secured by the knot 24 and the bolt 25. The inner end cap 22 has an exteriorly threaded neck 28 which is screwed into the threaded opening 12 in the air header it. The outer end cap 20 has secured thereto, as by welding, an eye 30.

As seen more clearly in Fig. 2, the core 16 is corrugated or fluted to provide alternate ridges 32 and valleys 34 extending longitudinally of the core. A plurality of orifices or openings 36 is provided in each of the valleys 34 for the passage of air or gas from the inside of the core 46 into the long small chambers 38 formed on the outer surface of the tube It by the alternating ridges and valleys 32 and 34, and by the windings it, which bridge the valleys 34.

The cord of the windings l8 may be formed of two or more strands of a suitable material such as a vinyl resin of the type commercially known as Saran, which is formed from a copolymer of vinyl chloride and vinylidine chloride. In the particular diffuser tube structure illustrated in Fig. 3, the winding cord 18 consists of three strands of the above-mentioned plastic material. These strands are tightly twisted in rope-like form, as illustrated in Fig. 4, and are wound sufficiently tightly so that adjacent turns of the winding are slightly compressed. In this manner there are created between adjacent turns 42a and 42b of the winding l8 a large number of very fine pores or passageways 44, forming a more or less uniform pattern through the interface between the adjacent turns.

As stated above, the diffuser tube structure illustrated in Figs. 1 through 4 of the drawing, and described above, constitutes in itself no part of the present invention, but is presented to aid in the understanding of the invention.

As further stated aove, there arises in the operation of plants employing such diffuser tubes a continuous problem of maintenance due to the necessity of periodically cleaning the tubes in order to prevent the occurrence of excessive pressure drops in the tubes, which would obviously interfere with the proper operation of the aeration process. The method commonly employed for such cleaning is the application of high pressures to the tubes from the inside. This application of pressure is commonly preceded by pretreatment of the tube with strong agents such as acid or alkali cleaning solutions, the tube being bathed in the solution. The soil is then flushed from the tube by applying a fluid pressure, either of a gas such as air or a liquid such as water, or a mixture thereof, to the interior of the tube.

It is found that such methods are not only highly laborious, but are additionally relatively ineffective in cleaning diffuser tubes of the type illustrated in Figs. 1 to 4 of the drawing and described above. Although the exact reasons for itself have sufficient detergent the failure of such prior art methods to produce satisfactory cleaning of the tubes are not precisely known, it is believed that the difficulty is due to the fact that any cleaning agent which is sufiiciently strong to dissolve the soil or to disperse the soil into suficiently fine particles to pass through the extremely fine pores if, is likewise sufficiently strong to Carbonize and fix organic materials lodged in and on the diffuser tube. Thus it is believed that the bathing of the tube in even the strong solutions heretofore employed leaves much of the soil in the form of finely dispersed particles in the elongated chambers 38. As the liquid cleaning agent is poured off upon removal of the tube from the cleaning solution, much of this soil is again deposited upon the interior surfaces of the windings i3 and the surface of the valleys or flutes 33. When fluid pressure is subsequently applied to the diffuser tube, either by the application of high air pressure, or by the insertion of water under pressure, in an attempt to blow the particles of soil out through the pores 44, the soil is again deposited in the pores and formed into small masses which partially block the porous wrapping. It has been found that a considerable number of cycles of this type of cleaning operation are required for complete cleaning of the tube and restoration of the flow resistance of the pores id to their original condition.

Generally, the method of the present invention resides in the discovery that by the application of a liquid, such as water, having a high velocity to the exterior surface of the tube, the liquid may be forced through the pores M into the chamhers 3E and thus flush out the chambers 38 through the apertures 36. The latter apertures 35 are much larger than the pores at, so that the soil particles trapped in the chambers 38 do not tend to accumulate at these apertures 36 but freely flow with the liquid into the interior of the core Hi. This discovery has enabled the present inventors to devise a method and apparatus for cleaning of diffuser tubes such as those above described which is far more simple and inexpensive than the methods and apparatus heretofore employed.

By applicants method of cleaning diffuser tubes, the tubes are first cleaned in a simple fashion on the exterior. In most cases, this may be done by ordinary flushing away of exterior soil with a common hose. The difiuser tube is then soaked in a detergent composition containing a surface-active agent for the purpose of loosening the soil from the inner surfaces of the windings l8 and the passageways or pores 44. This soaking is preferably continued for about 10 to 15 hours, but a somewhat shorter time may be employed if the tube is used under conditions where the soiling is extremely slight.

Any well-known type of detergent composition is suitable for use as a bath in loosening the soil which is present in the flutes and the pores. A cationic, anionic or non-ionic surface-active agent may be employed as the sole active constituent of a water solution, but improved results are achieved by the addition of a detergent assistant. In cases Where the soil adhering to the windings and the core is relatively easily removed, a solution of a detergent assistant may action to be satisfactory for employment as the detergent composition.

The preferred detergent compositions include a surface-active agent which is non-sudsing or has only low sudsing properties, preferably a non-ionic detergent such as that formed by reacting tall oil fatty acids with ethylene oxide. One such detergent is commercially known as MXP, sold by Monsanto Chemical Go. Other suitable surface-active agents are, for example: a sodium alkyl aryl sulfonate, such as is sold by Allied Chemical & Dye Corp. under the name Naccolene F. or Naccolene E; a fatty alcohol sulfate, such as is sold by E. I. du Pont de Nemours Co. under the name Duponol DLS; the dioctyl ester of sodium sulfosuccinic acid, such as is sold by American Cyanamid & Chemical Corp. under the name Aerosol OT; or a mixed fatty acid (Cm-C16) alkylolamine condensate such as is sold by Ninol Laboratories under the name Ninol 400. It will be understood that this listing constitutes only a small fraction of the surfaceactive agents which may be employed in the detergent composition, any of the surface-active agents well known for analogous uses giving reasonably satisfactory results.

The detergent or detergent assistant which be used in the detergent composition may be, for example: anhydrous or hydrated sodium metasilicate, such as that sold, respectively, as Drymet and Escomet by Cowles Detergent 00.; sodium hexametaphosphate, such as that sold as Calgon by Calgon, Inc.; tetrasodium pyrophosphate, such as sold by Monsanto Chemical (70. under the name Phosphatex; trisodium phosphate; sodium triphosphate; sodium carbonate; sodium metaphcsphate, and the like.

The preferred detergent composition for the practice of the method of the invention consists of a water solution of 2% MXP (a product of reaction of tall oil fatty acids with ethylene oxide, mentioned above) and 2% sodium metasilicate.

Following the detergent bath, all portions of the exterior surface of the diffuser tube are then sprayed with water having a velocity of at least 40 feet per second, and preferably of a velocity of greater than 80 feet per second. It is important to note that this spraying operation (involving the impingement of a multiplicity of water jets on the tube) is preferably carried out with the open neck l2 suspended downwardly. This is desirable in order that the water in the elongated chambers 38 will flow freely out of the tube, thus completely and rapidly flushing out through the openings 36 the dirt particles loosened by the bath in the detergent composition. It is found that by this method, the tubes may be cleaned with as little as 30 to 60 seconds of application of the water spray. Such a short application of water jets has been found to re store even the most badly soiled of diffuser tubes employed in the activated sludge sewage process to their original pressure drop conditions after the preliminary washing of the exterior, and bathing of the tubes in a suitable detergent composition. In the case of badly soiled tubes, the preliminary step of cleaning the exterior of the tube prior to the bath in the detergent composition is performed with high velocity jets similar to those employed in the final step, rather than with an ordinary hose, which is, however, suitable where the tube is only mildly soiled. I

There is illustrated in Figs. 5 through 8 one manner in which the high velocity spraying of the present invention may be performed, and a simple, inexpensive and efiicient apparatus for this purpose. As shown in these figures, the high velocity spraying process is carried out in acylindrical tank 50 having at the bottom thereof a drain 52. A spray jet assembly, generally designated by the numeral 54, is supported in the interior of the tank 50 near the top thereof by a support bracket 56 which rests on the edge of the tank 50, and on the diametrically opposite side by an inlet pipe 58 which is supported by and extends out through an aperture 60 in the wall of the tank 5!].

The inner end of the bracket 56 is secured as by a weld 62 to the outer surface of a short tubular member 64. The diametrically opposed portion of the tube -64 is provided with a coupling '65 receiving the input pipe 58. Coaxial with the tube 54 is a second short tubular member $8 of smaller diameter. Secured to the upper edges of the tubes 6d and 68, as by welding, is an annular plate is having an outer diameter equal to the diameterof the tube 64 and an inner diameter gomewhat smaller than the diameter of the tube Secured to the bottom ends of the tube members 64 and $8 is an annular plate 12, thus forming an annular water ring 80. The plate 12 has bored therein a circular series of passages M extended generally inwardly and downwardly from the upper face of the plate to the inner face thereof, the inner face 16 being bevelled so that the orifices or bores 14 are substantially perpendicular to the inner face 16. The bores M are inclined downwardly to form an angle of approximately 60 degrees with the axis of the tubes 64 and 68.

The inner edge 18 of the upper annular plate It serves to maintain the centered position of the diffuser tube [4 as it is passed through the assembly 54, as shown in Fig. 8. The downward inclination of the bores 14 has been found desirable in order to avoid the possibility of compacting soil remaining after the preliminary cleaning, into the outer portions of the pores 44. By sparying at an angle with respect to the axis of the tube it is assured that soil remaining on the outer surface will be washed off, rather than forced into the pores 44. However, the angle at which the jets intercept the axis of the tube must not be less than 45 degrees, since lesser angles of incidence result in failure to properly flush the interior of a diffuser tube. Therefore, the angle at which the jet strikes the diffuser tubes should be between 45 degrees and 90 degrees and is preferably 60 degrees, as in the illustrated embodiment. The bevelling of the inner face serves to maintain the jets at the proper angle without the dispersion which has been found to occur in the absence of such bevelling.

The number of jets or orifices M is sufficient to secure complete coverage of the surface of a diffuser tube i4 inserted in the central aperture in the upper plate l0. Preferably, the number of equally spaced jets or apertures 14 corresponds exactly to the number of flutes or chambers 38 on the surface of the tube core l6.

In a particular embodiment of the apparatus illustrated in Figs. 5 through 8, the jets M were approximately inch in diameter; the water pressure maintained at the inlet pipe 58 was between 40 and 50 pounds per square inch; and the velocity of the jets of water incident upon the windings [6 of the tube M was approximately feet per second.

In a typical practice of the method of the invention with the apparatus shown in Figs. 5 through 8 in an activated sludge processing plant, the tubes are sprayed down with an ordinary hose as the first step of the operation, the tubes which are exceedingly soiled being instead passed through the jet apparatus illustrated. Thereafter the tubes are soaked overnight in a solution of 2% MXP referred to above) and 2% sodium metasilicate in water. The tubes are then lowered through the assembly 54 and pulled back up, in a time of approximately 30 to 60 seconds, a cord (not shown) tied to eye 38 being used to facilitate this operation. It is then found that all of the tubes irrespective of the condition of soil existing before the cleaning process, have been restored to their original pressure loss which was, with one construction of diffuser tube in accordance with Figs. 1 to 4, about 8 /2 inches of water with an air flow rate of 6 cubic feet per minute.

There has been described above the general principles and practices of the invention in conjunction with a particular embodiment of the invention in order to aid in the understanding thereof. It will, of course, be understood that the particular embodiment illustrated is not in itself definitive of the scope of the invention. Therefore, the invention is not to be restricted to the exact structure of the illustrative embodiment described above. Nor is the invention to be limited to the precise steps of the method described above, since obvious variations in these steps will readily suggest themselves to skilled workers in the art.

We claim:

1. A method of cleaning a diffuser tube comprising a hollow foraminated elongated core open at least at one end and having longitudinal outer flutes and a tight winding of non-circular twisted cord on said core forming reticulated pores, said method comprising the steps of progressively moving the tube relative to a plurality of water jets having a velocity of at least 40 feet per second, spraying the exterior surface of the tube with said water jets at an angle of approximately 60 degrees with respect to the axis of the tube in the direction of relative motion of the tube, to clean the outer surface of the tube, soaking the tube in a detergent to loosen soil in the flutes and pores, and again spraying the exterior surface of the tube in the manner aforesaid with the tube vertically disposed and said open end directed downwardly, to flush the soil so loosened through the foramina of the core.

2. A method of cleaning a diffuser tube comprising a hollow foraminated elongated core open at least at one end and having longitudinal outer flutes and a tight winding of non-circular twisted cord on said core forming reticulated pores, said method comprising the steps of progressively moving the tube relative to a plurality of of water jets having a velocity of at least 40 feet per second, spraying the exterior surface of the tube with said water jets at an angle of less than 90 degrees and greater than 45 degrees with respect to the axis of the tube in the direction of relative motion of the tube, to clean the outer surface of the windings, soaking the tube in a detergent composition to loosen soil in the flutes and again spraying the exterior surface of the tube in a manner aforesaid with the tube vertically disposed and said open end directed downwardly, to flush the soil so loosened through the foramina of the core.

3. A method of cleaning a diffuser tube comprising a hollow foraminated elongated core having surface recesses and a tight winding of non-circular twisted cord on said core forming reticulated pores, said method comprising the steps of soaking the tube in a detergent composition to loosen soil in the recesses and pores, pro gressively moving the tube relative to a plurality of liquid jets having a velocity of at least 40 feet per second, and spraying the exterior surface of the tube with said liquid jets at an angle of less than degrees and greater than 45 degrees with respect to the axis of the tube in the direction of relative motion of the tube, to flush the soil so loosened through the foramina of the core.

4. A method of cleaning a diffuser tube comprising a hollow foraminated core having surface recesses and a porous wrapping on said core, said method comprising the steps of soaking the tube in a detergent composition to loosen soil in the recesses and pores, progressively moving the tube relative to a plurality of liquid jets having a velocity of at least 40 feet per second, and spraying the exterior surface of the tube with said liquid jets in the direction of relative motion of the tube, to flush the soil so loosened through the foramina of the core.

5. A method of cleaning a foraminated diffuser element through which an aeriform body may be forced under pressure and difiused in the surrounding medium, said method comprising the steps of soaking the diffuser element in a detergent composition to loosen soil in the foramina of the diffuser element, progressively moving the diffuser element relative to a plurality of liquid jets having a velocity of at least 40 feet per second, and spraying said diffuser element with said liquid jets in the direction of relative motion of the diffuser element.

6. A method of cleaning a foraminated diffuser element through which an aeriform body may be forced under pressure and diffused in the surrounding medium, said method comprising the steps of progressively moving the diffuser element relative to a plurality of liquid jets having a velocity of at least 40 feet per second, and spraying said diffuser element with said liquid jets in the direction of relative motion of the diffuser element.

7. The method of cleaning a foraminated diffuser element through which an aeriform body may be forced under pressure and diffused into the surrounding medium, said method comprising the steps of progressively moving the element relative to a plurality of liquid jets having a velocity of at least 40 feet per second, spraying the exterior surface of the element with said liquid jets at an angle of approximately 60 degrees with respect to the axis of the element in the direction of relative motion of the element, to clean the outer surface of the element, soaking the element in a detergent to loosen soil in the foramina, and again spraying the exterior surface of the element in the manner aforesaid to flush the soil so loosened through the foramina of the element.

8. The method of cleaning a foraminated diffuser element through which an aeriform body may be forced under pressure and diffused into the surrounding medium, said method comprising the steps of progressively moving the element relative to a plurality of liquid jets having a velocity of at least 40 feet per second, spraying the exterior surface of the element with said liquid jets at an angle of less than'90 degrees and greater than 45 degrees with respect to the axis of the element in the direction of relative motion of the element, to clean the outer surface of the element, soaking the element in a detergent composition to loosen soil in the foramina, and again spraying the exterior surface of the element in the manner aforesaid to flush the soil so loosened through the foramina of the element.

9. The method of cleaning a foraminated diffuser element through which an aeriform body may be forced under pressure and diffused into the surrounding medium, said method comprising the steps of soaking the element in a detergent composition to loosen soil in the foramina, progressively moving the element relative to a plurality of liquid jets having a velocity of at least 40 feet per second, and spraying the exterior surface of the element with said liquid jets at an angle of less than 90 degrees and greater than 45 degrees with respect to the axis of the element in the direction of relative motion of the element to flush the oil so loosened through the foramina of the element.

References Cited in the file of this patent UNITED STATES PATENTS Number Re. 3,870 415,935 908,509 1,018,046 1,161,467 1,200,289 1,266,167 1,498,061 1,698,858 1,913,885 2,009,078 2,261,560 2,340,325

Name Date Hallowell Mar. 8,1870 Boynton et a1 Nov. 26, 1889 Silverglade Jan. 5, 1909 Goldman Feb. 20, 1912 Gallup Nov. 23, 1915 Wittemann Oct. 3, 1916 Sears May 14, 1918 Adams June 17, 1924 Smith Jan. 15, 1929 Jordahl June 13, 1933 Ziska July 23, 1935 Pellas et a1 Nov. 4, 1941 Harrigan Feb. 1, 1944 

1. A METHOD OF CLEANING A DIFFUSER TUBE COMPRISING A HOLLOW FORAMINATED ELONGATED CORE OPEN AT LEAST AT ONE END AND HAVING LONGITUDINAL OUTER FLUTES AND A TIGHT WINDING OF NON-CIRCULAR TWISTED CORD ON SAID CORE FORMING RETICULATED PORES, SAID METHOD COMPRISING THE STEPS OF PROGRESSIVELY MOVING THE TUBE RELATIVE TO A PLURALITY OF WATER JETS HAVING A VELOCITY OF AT LEAST 40 FEET PER SECOND, SPRAYING THE EXTERIOR SURFACE OF THE TUBE WITH SAID WATER JETS AT AN ANGLE OF APPROXIMATELY 60 DEGREES WITH RESPECT TO THE AXIS OF THE TUBE IN THE DIRECTION OF RELATIVE MOTION OF THE TUBE, TO CLEAN THE OUTER SURFACE OF THE TUBE, SOAKING THE TUBE IN A DETERGENT TO LOOSEN SOIL IN THE FLUTES AND PORES, AND AGAIN SPRAYING THE EXTERIOR SURFACE OF THE TUBE IN THE MANNER AFORESAID WITH THE TUBE VERTICALLY DISPOSED AND SAID OPEN END DIRECTED DOWNWARDLY, TO FLUSH THE SOIL SO LOOSENED THROUGH THE FORAMINA OF THE CORE. 